Ethanol for industrial use is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulose materials, such as corn or sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulose materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulose material, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol for fuels or consumption. In addition, fermentation of starchy or cellulose materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Conventional ethanol compositions are formed as a result of the above-identified processes that contain impurities which must be removed.
For example, U.S. Pat. No. 5,488,185 utilizes a petrochemical feed stock and relates to an ethene stream which contains ethane as an impurity or a propene stream which contains propane as an impurity that is hydrated with water vapor in the presence of a hydration catalyst to produce ethanol or isopropanol, respectively. After removal of the alcohol the gaseous product stream is subjected to adsorption, thereby producing an ethene-enriched stream or a propene-enriched stream. The ethene-enriched stream or the propene-enriched stream is recycled to the hydration reactor.
U.S. Pat. Nos. 5,185,481 and 5,284,983 relate to conventional fermentation methods for producing ethanol. The produced ethanol compositions comprise impurities such as methanol, acetaldehyde, n-propanol, n-butanol, ethyl acetate, 3-methylbutanol, diethyl ether, acetone, secondary butanol, and crotonaldehyde. These references also disclose separation methods for treating the crude ethanol aqueous solution with an extracting solvent comprising carbon dioxide in a liquid state or carbon dioxide in a super-critical state.
U.S. Pat. Nos. 5,445,716; 5,800,681; and 5,415,741 relate to separation methods for mixtures of ethanol and isopropanol. Ethanol is difficult to separate from isopropanol by conventional distillation or rectification because of the proximity of their boiling points. Ethanol can be readily separated from isopropanol by extractive distillation. Effective extractive agents are dipentene, anisole, and ethyl benzene. The mixtures in these references, comprise a significant amount of isopropanol, e.g., at least 21.5 wt. % isopropanol.
Also, U.S. Pat. No. 5,858,031 relates to a method for enhancing the visibility of a flame produced during free-burning of an aqueous alcohol-based fuel composition in air. The fuel includes between approximately 10% and 30% by volume of water, and between approximately 70% and 90% by volume of a mixture of alcohols including ethanol and isopropanol, the ethanol constituting between approximately 24% and 83% by volume of the fuel composition. The method includes providing an amount of isopropanol ranging between approximately 7% and 60% by volume of the fuel composition, in which the volume ratio of isopropanol to ethanol in the fuel does not exceed 2:1.
U.S. Pat. No. 5,081,321 relates to isopropanol preparation through catalytic hydrogenation of acetone. The reaction may preferably be effected at a temperature of from room temperature to 200° C., although an industrial reaction rate is achieved at a reaction temperature of from 35 to 150° C. Too high of a reaction temperature induces excess hydrogenation decomposition of acetone, resulting in reduced yields of isopropanol.
Although conventional processes may produce and/or purify ethanol compositions, these processes rely on petrochemical feed stocks or fermentation techniques to yield the ethanol compositions. Further, in the resultant ethanol compositions that do comprise isopropanol, the isopropanol is present in large amounts.
Therefore, the need exists for an ethanol production process that reduces and/or controls isopropanol content.